1. Department of Civil Engineering, Southwest Forestry University, Kunming 650224, China 2. Department of Civil Engineering, University of Kentucky, Lexington, KY 40506-0281, USA 3. Shanghai Geotechnical Investigations & Design Institute Company Limited, Shanghai 200032, China
Empirical data on deep urban excavations can provide designers a significant reference basis for assessing potential deformations of the deep excavations and their impact on adjacent structures. The construction of the Shanghai Center involved excavations in excess of 33-m-deep using the top-down method at a site underlain by thick deposits of marine soft clay. A retaining system was achieved by 50-m-deep diaphragm walls with six levels of struts. During construction, a comprehensive instrumentation program lasting 14 months was conducted to monitor the behaviors of this deep circular excavation. The following main items related to ground surface movements and deformations were collected: (1) walls and circumferential soils lateral movements; (2) peripheral soil deflection in layers and ground settlements; and (3) pit basal heave. The results from the field instrumentation showed that deflections of the site were strictly controlled and had no large movements that might lead to damage to the stability of the foundation pit. The field performance of another 21cylindrical excavations in top-down method were collected to compare with this case through statistical analysis. In addition, numerical analyses were conducted to compare with the observed data. The extensively monitored data are characterized and analyzed in this paper.
Construct the first level wall and retaining structure framework with 1 m height as preparation work; 07/27/2009–08/24/2009
Cast concrete; 08/25/2009–08/27/2009
53
2&3
The Second level strut (Elevation−8.5 to−14.5 m)
Remove the first level soil to form a pit with a size of 50m (length) × 15m (width) × 5m (depth) around the lift platform No. 1; 09/16/2009–09/22/2009
Excavate to the bottom of the second level strut with a depth of 10 m around the lift platform No. 3 in a direction of north-south from peripheral to central; 10/05/2009–10/11/2009
Change excavation sequence, excavate in the direction of east-west from central to peripheral;10/11/2009–10/23/2009
Construct the second level wall and retaining structure framework and cast concrete; 10/24/2009–10/30/2009
45
4
The Third level strut (Elevation−14.5 to−19.5 m)
Excavate to the third level along the circumference but do not remove the central soil; 10/31/2009–11/03/2009
Construct the third level wall and retaining structure framework and cast concrete; 11/04/2009–11/16/2009
18
5
The Fourth level strut (Elevation−19.5 to−24.0 m)
Remove the central soil at the third level; 11/17/2009–11/21/2009
Begin to dewater; 11/22/2009
Excavate along the circumference to the fourth level but do not remove the central soil; 11/22/2009–11/29/2009
Construct the fourth level wall and retaining structure framework and cast concrete; 11/30/2009–12/07/2009
Remove the central soil at the fourth level; 12/08/2009–12/14/2009
28
6
The Fifth level strut (Elevation−24.0 to−28.0 m)
Excavate along the circumference to the fifth level but do not remove the central soil; 12/15/2009–12/20/2009
Construct the fifth level wall and retaining structure framework and cast concrete; 15/21/2009–01/04/2010
14
7
The Sixth level strut (Elevation−28.0 to−33.7 m)
Remove the central soil at the fifth level; 01/05/2010-01/08/2010
Excavate along the circumference to the sixth level but do not remove the central soil; 01/09/2010–01/23/2010
Construct the sixth level wall and retaining structure framework and cast concrete; 01/24/2010–01/30/2010
25
8
Cast concrete under-layer
Remove the central soil at the sixth level and excavate to-33.7m; 01/31/2010–02/03/2010
Cast all concrete under-layer; 02/04/2010–02/12/2010
9
9
Base plate construction
Construct the base plate framework and cast concrete; 02/08/2010–04/19/2010
End dewatering; 04/05/2010
71
10
Underground Construction
Construct the underground structure and facilities; 04/20/2010–09/29/2010
161
Tab.1
Level
Size, height × thickness (mm × mm)
Central elevation (m)
1
3700 × 1500
−1.75
2
2800 × 1500
−9.30
3
2800 × 1600
−15.30
4
3000 × 1600
−20.30
5
3000 × 1800
−24.90
6
3000 × 1800
−28.90
Tab.2
Fig.4
Fig.5
Fig.6
depth (m)
accumulative settlement (mm)
average (mm)
R1
R2
R3
R4
R5
R6
R7
R8
−6.0
−57
−48
−49
−49
−58
−46
−41
−41
−48
−11.0
−24
−41
−48
−48
−60
−42
−44
−39
−42
−16.0
-−20
−19
−41
−41
−46
−38
−38
−29
−33
−21.0
−5
−7
−29
−29
−37
−27
−27
−17
−21
−26.0
−5
4
−20
−20
−4
−4
−7
−12
−7
−31.0
4
10
−5
−5
3
-2
-5
1
1
−36.0
7
9
8
8
4
4
2
−2
5
−41.0
13
19
12
12
15
7
−1
4
10
-46.0
18
15
15
15
20
12
9
3
13
-51.0
17
10
13
13
20
17
17
3
14
-56.0
18
16
20
20
22
18
19
10
18
Tab.3
Fig.7
Fig.8
Fig.9
Fig.10
Fig.11
Fig.12
Fig.13
: unit weight of soil (kN/m3);
: effective cohesion(kPa);
: effective friction angle(°);
v: Poisson’s ratio (dimensionless unit);
K: permeability coefficient(10-4cm/s);
Em: pressure meter modulus(MPa);
Gm: pressure meter shear modulus(MPa);
Ps:bearing capacity of static penetration test(MPa);
E: dynamic elastic modulus (MPa);
G: dynamic shear modulus (MPa);
H: excavation depth of the pit(m);
: the maximum lateral movements of the walls (mm);
: the depth whereoccurred (m);
D: foundation pit diameter (m);
Hd: embedded length of the retaining walls (m);
: the maximum lateral movement of the circumferential soil (mm) ;
: the maximum layered soil settlement (mm) ;
: the maximum basal heave (mm) ;
1
Ou C Y, Liao J T, Lin H D. Performance of diaphragm wall constructed using the top-down method. Journal of Geotechnical and Geoenvironmental Engineering, 1998, 124(9): 798–808 https://doi.org/10.1061/(ASCE)1090-0241(1998)124:9(798)
2
Liu G B, Ng C W, Wang Z W. Observed performance of a deep multistrutted excavation in Shanghai soft clays. Journal of Geotechnical and Geoenvironmental Engineering, 2005, 131(8): 1004–1013 https://doi.org/10.1061/(ASCE)1090-0241(2005)131:8(1004)
3
Tan Y, Wang D. Characteristics of a large-scale deep foundation pit excavated by the central-island technique in Shanghai soft clay. II: top-down construction of the peripheral rectangular pit. Journal of Geotechnical and Geoenvironmental Engineering, 2013a, 139(11): 1894–1910 https://doi.org/10.1061/(ASCE)GT.1943-5606.0000929
4
Whittle A J, Corral G, Jen L C, Rawnsley R P. Predication and performance of deep excavations for Courthouse Station, Boston. Journal of Geotechnical and Geoenvironmental Engineering, 2015, 141(4): 04014123 https://doi.org/10.1061/(ASCE)GT.1943-5606.0001246
5
Orazalin Z Y, Whittle A J, Olsen M B. Three-dimensional analysis of excavation support system for the Stata Center Basement on the MIT campus. Journal of Geotechnical and Geoenvironmental Engineering, 2015, 141(7): 05015001 https://doi.org/10.1061/(ASCE)GT.1943-5606.0001326
6
Tanner Blackburn J, Finno R J. Three-dimensional responses observed in an internally braced excavation in soft clay. Journal of Geotechnical and Geoenvironmental Engineering, 2007, 133(11): 1364–1373 https://doi.org/10.1061/(ASCE)1090-0241(2007)133:11(1364)
7
Hashash Y M A, Osouli A, Marulanda C. Central artery/tunnel project excavation induced ground deformations. Journal of Geotechnical and Geoenvironmental Engineering, 2008, 134(9): 1399–1406 https://doi.org/10.1061/(ASCE)1090-0241(2008)134:9(1399)
8
Tan Y, Wang D. Characteristics of a large-scale deep foundation pit excavated by the central-island technique in Shanghai soft clay. I: bottom-up construction of the central cylindrical shaft. Journal of Geotechnical and Geoenvironmental Engineering, 2013b, 139(11): 1875–1893 https://doi.org/10.1061/(ASCE)GT.1943-5606.0000928
9
Wong I, Poh T, Chuah H. Performance of excavations for depresses expressway in Singapore. Journal of Geotechnical and Geoenvironmental Engineering, 1997, 123(7): 617–625 https://doi.org/10.1061/(ASCE)1090-0241(1997)123:7(617)
10
Hsieh P G, Ou C Y. Shape of ground surface settlement profiles caused by excavation. Canadian Geotechnical Journal, 1998, 35(6): 1004–1017 https://doi.org/10.1139/t98-056
Moormann C. Analysis of wall and ground movements due to deep excavations in soft soil based on a new worldwide database. Soil and Foundation, 2004, 44(1): 87–98 https://doi.org/10.3208/sandf.44.87
13
O’Rourke T D, McGinn A J. Lessons learned for ground movements and soil stabilization from the Boston Central Artery. Journal of Geotechnical and Geoenvironmental Engineering, 2006, 132(8): 966–989 https://doi.org/10.1061/(ASCE)1090-0241(2006)132:8(966)
14
Wang J H, Xu Z H, Wang W D. Wall and ground movements due to deep excavations in Shanghai soft soils. Journal of Geotechnical and Geoenvironmental Engineering, 2010, 136(7): 985–994 https://doi.org/10.1061/(ASCE)GT.1943-5606.0000299
15
Tan Y, Wei B. Observed behaviors of a long and deep excavation constructed by cut-and-cover technique in Shanghai soft clay. Journal of Geotechnical and Geoenvironmental Engineering, 2012, 138(1): 69–88 https://doi.org/10.1061/(ASCE)GT.1943-5606.0000553
16
Tan Y, Wang D. Structural behaviors of large underground earth-retaining systems in Shanghai I: unpropped circular diaphragm wall. Journal of Performance of Constructed Facilities, 2015a, 29(2): 04014058 https://doi.org/10.1061/(ASCE)CF.1943-5509.0000521
17
Tan Y, Wang D. Structural behaviors of large underground earth-retaining systems in Shanghai. II: multipropped rectangular diaphragm wall. Journal of Performance of Constructed Facilities, 2015b, 29(2): 04014059 https://doi.org/10.1061/(ASCE)CF.1943-5509.0000535
18
Shanghai Construction and Management Commission. Code for Investigation of Geotechnical Engineering (DGJ08-37-2002), Shanghai: Jian Zhu Jian Cai Ye Shi Chang Guan Li Zong Zhan, 2002 (in Chinese)
19
Xu Y S, Shen S L, Du Y J. Geological and hydrogeological environment in Shanghai with geohazards to construction and maintenance of infrastructures. Engineering Geology, 2009, 109(3-4): 241–254 https://doi.org/10.1016/j.enggeo.2009.08.009
20
Clough G W, O’Rourke T D. Construction induced movements of in-situ walls. Geotechnical Special publication: Design and performance of earth retaining structures (GSP25), ASCE, Reston, VA, 1990
21
Kung G T C, Juang C H, Hsiao E C L, Hashash Y M A. Simplified model for wall deflection and ground-surface settlement caused by braced excavation in clays. Journal of Geotechnical and Geoenvironmental Engineering, 2007, 133(6): 731–747 https://doi.org/10.1061/(ASCE)1090-0241(2007)133:6(731)
22
Liu K X. Three dimensional analysis of deep excavation in soft clay. M.Eng. thesis, National University of Singapore, 1995
23
Lee F, Yong K, Quan K, Chee K. Effect of corners in strutted excavations: field monitoring and case histories. Journal of Geotechnical and Geoenvironmental Engineering, 1998, 124(4): 339–349 https://doi.org/10.1061/(ASCE)1090-0241(1998)124:4(339)
24
Liu G B, Jiang R J, Ng C, Hong Y. Deformation characteristics of a 38m deep excavation in soft clay. Canadian Geotechnical Journal, 2011, 48(12): 1817–1828 https://doi.org/10.1139/t11-075
25
Peck R B. Deep excavation and tunneling in soft grund. In: Proceedings of the 7th International Conference of Soil Mechanics and Foundation Engineering, Mexico City, 1969, 225–281